For the characters of 'Ed, Edd n Eddy', he made the kids' tongues different colors after seeing his son and his friends come home with candy and noticed the colors of their tongues.
Is strictly against ad-libbing; all of Ed's non-sequiturs were scripted.
Based the 'Ed, Edd n Eddy' episode "Pop Goes the Ed" on an experience from childhood where he was talked into going to a pool party and was given a bathing suit that was several sizes too small; the bathing suit snapped off as a result.